Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/14—Secondary fibres
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
  • B09B3/30—Destroying solid waste or transforming solid waste into something useful or harmless involving mechanical treatment
  • B09B3/38—Stirring or kneading
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
  • B09B3/70—Chemical treatment, e.g. pH adjustment or oxidation
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
  • D21B1/00—Fibrous raw materials or their mechanical treatment
  • D21B1/04—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres
  • D21B1/12—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres by wet methods, by the use of steam
  • D21B1/30—Defibrating by other means
  • D21B1/32—Defibrating by other means of waste paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
  • D21C5/02—Working-up waste paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
  • D21C5/02—Working-up waste paper
  • D21C5/022—Chemicals therefor
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
  • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B2101/00—Type of solid waste
  • B09B2101/65—Medical waste
  • B09B2101/67—Diapers or nappies

Definitions

• the present invention relates to a method for producing recycled pulp from used sanitary goods.
• the present invention relates to a method of recovering pulp fibers from a sanitary article such as a used disposable paper diaper containing pulp fibers and a superabsorbent polymer, and producing a recycled pulp that can be reused as a sanitary article.
• used sanitary goods such as disposable disposable diapers.
• used sanitary goods are decomposed in water, separated into components of sanitary goods, and recovered.
• the superabsorbent polymer contained in the sanitary article absorbs moisture and increases its mass, and also becomes a gel and loses fluidity, thereby reducing the processing capability of the processing apparatus.
• Patent Document 1 discloses dehydration of superabsorbent polymers in used paper diapers that have absorbed moisture with lime (Claim 2). This reduces the weight of the superabsorbent polymer and restores the fluidity from the gel state to the original state, thereby avoiding a reduction in processing capacity of the processing apparatus (paragraph [0020]).
• Patent Document 2 discloses a recycling method of used diapers in which the superabsorbent polymer contained in the paper diaper can be formed into fine particles without using any chemicals when recycling the used paper diaper. Disclosure.
• the recycling method breaks a used paper diaper and decomposes it into a pulp component and a non-pulp component. After washing the mixture of the decomposed pulp component and a non-pulp component such as vinyl with water, the non-pulp component is removed from the mixture.
• Patent Document 2 further discloses that the used paper diaper is sterilized and deodorized using an ultraviolet lamp, ozone (gas), ozone water, or the like in the measuring step (paragraph [0015]).
• a superabsorbent polymer dehydrated using lime becomes a solid powder having a particle size of several ⁇ m to several hundred ⁇ m, and particularly fine particles are easily caught between pulp fibers, It cannot be completely removed by simple water washing.
• the recovered pulp fiber not only the remaining superabsorbent polymer becomes a foreign substance but also a calcium salt, so the recovered pulp fiber is hygienic. Ashes more than the product standard value are easily detected. Moreover, it becomes strong alkalinity by lime use, and when ozone treatment is performed, ozone becomes easy to deactivate.
• the superabsorbent polymer broken into fine particles of 10 ⁇ m or less by a pulverizer is easy to get caught between pulp fibers because of fine particles, and can be completely removed only by physical washing. I can't remove it.
• the recovered pulp fiber is to be reused, the remaining superabsorbent polymer becomes a foreign matter.
• the highly water-absorbing polymer that absorbs water is pulverized by a pulverizer, a lot of labor, pulverization equipment and processing energy are required, resulting in poor production efficiency.
• the present invention has been made by paying attention to such a conventional problem, and the used hygiene product has an aqueous solution containing a polyvalent metal ion capable of suppressing the water-absorbing expansion of the superabsorbent polymer, or has a pH of 2. Decomposed in an acidic aqueous solution of .5 or less, separated into pulp fibers (including residual superabsorbent polymer) and other materials, and the separated pulp fibers are treated with ozone in an acidic aqueous solution having a pH of 2.5 or less. Thus, it was found that the superabsorbent polymer remaining in the separated pulp fibers can be efficiently decomposed and removed by ozone, and recycled pulp that can be reused as sanitary goods can be obtained, thereby completing the present invention.
• the present invention is a method for recovering pulp fibers from used sanitary goods including pulp fibers and a superabsorbent polymer, and producing recycled pulp that can be reused as sanitary goods, the method comprising:
• the used sanitary goods are made into pulp fiber and other materials by applying physical force to the used sanitary goods in an aqueous solution containing polyvalent metal ions or an acidic aqueous solution having a pH of 2.5 or less.
• the process of breaking down into It includes a step of separating pulp fibers from a mixture of pulp fibers and other materials produced in the decomposition step, and a step of treating the separated pulp fibers with an ozone-containing aqueous solution having a pH of 2.5 or less.
• a method of recovering pulp fibers from used sanitary products including pulp fibers and a superabsorbent polymer, and producing recycled pulp that can be reused as sanitary products comprising:
• the used sanitary goods are made into pulp fiber and other materials by applying physical force to the used sanitary goods in an aqueous solution containing polyvalent metal ions or an acidic aqueous solution having a pH of 2.5 or less.
• the process of breaking down into A method comprising separating pulp fibers from a mixture of pulp fibers and other materials generated in the decomposition step, and treating the separated pulp fibers with an ozone-containing aqueous solution having a pH of 2.5 or less. .
• the process of breaking down into Recycling characterized in that it includes a step of separating pulp fibers from a mixture of pulp fibers and other materials produced in the decomposition step, and a step of treating the separated pulp fibers with an ozone-containing aqueous solution having a pH of 2.5 or less pulp.
• ash pulp that conforms to the sanitary material standards can be efficiently recovered from used sanitary goods.
• the present invention relates to a method for recovering pulp fibers from used sanitary products including pulp fibers and superabsorbent polymers and producing recycled pulp that can be reused as sanitary products.
• the sanitary article is not particularly limited as long as it contains pulp fibers and a superabsorbent polymer, and examples thereof include disposable diapers, incontinence pads, urine removing pads, sanitary napkins, panty liners, and the like. Of these, incontinence pads and disposable diapers that are collected together in a facility or the like are preferable because they do not require separation and have a relatively large amount of pulp.
• a fluffy pulp fiber Although it does not specifically limit as a pulp fiber, A fluffy pulp fiber, a chemical pulp fiber, etc. can be illustrated.
• Superabsorbent polymer also called SAP (Superabsorbent Polymer)
• SAP Superabsorbent Polymer
• pulp produced by the method of the present invention is referred to as “recycled pulp”.
• the method of the present invention comprises: The used sanitary article is made into pulp fiber and other materials by applying physical force to the used sanitary article in an aqueous solution containing polyvalent metal ions or an acidic aqueous solution having a pH of 2.5 or less.
• the process of breaking down into A step of separating the pulp fiber from the mixture of the pulp fiber and other materials generated in the decomposition step, and a step of treating the separated pulp fiber with an ozone-containing aqueous solution having a pH of 2.5 or less.
• the method of the present invention preferably further comprises a step of dewatering the separated pulp fibers.
• the method of the present invention is a method for treating used hygiene articles by applying physical force to the used hygiene articles in an aqueous solution containing polyvalent metal ions or an acidic aqueous solution having a pH of 2.5 or less. It includes a step of breaking down into pulp fibers and other materials (hereinafter also referred to as “decomposing step”).
• the used sanitary product is decomposed into pulp fibers and other materials by applying physical force to the used sanitary product.
• Sanitary goods are usually composed of materials such as pulp fibers, superabsorbent polymers, non-woven fabrics, plastic films, and rubber.
• used sanitary goods are decomposed into the above-mentioned materials.
• the degree of decomposition is not limited as long as at least a part of the pulp fiber can be recovered, and may not be complete or may be partial.
• the method of applying a physical force to the used sanitary goods is not limited, and examples thereof include stirring, hitting, thrusting, vibration, tearing, cutting, crushing, and the like. Of these, stirring is preferred. Stirring can be performed in a treatment tank equipped with a stirrer such as a washing machine.
• This decomposition step is performed in an aqueous solution containing polyvalent metal ions or an acidic aqueous solution having a pH of 2.5 or less.
• an aqueous solution containing a polyvalent metal ion or an acidic aqueous solution having a pH of 2.5 or less the superabsorbent polymer swollen by absorbing water in the used sanitary goods is dehydrated.
• a superabsorbent polymer has a hydrophilic group (for example, —COO ⁇ ), and a water molecule is bonded to the hydrophilic group through a hydrogen bond, so that a large amount of water can be absorbed.
• a superabsorbent polymer that absorbs water When a superabsorbent polymer that absorbs water is placed in an aqueous solution containing a polyvalent metal ion such as calcium ion, the polyvalent metal ion is bonded to a hydrophilic group (for example, —COO ⁇ ) (for example, —COO—Ca—OCO). -), The hydrogen bond between the hydrophilic group and the water molecule is broken, the water molecule is released, the superabsorbent polymer is dehydrated, and the superabsorbent polymer that has absorbed water is dissolved in an acidic aqueous solution of pH 2.5 or less.
• a hydrophilic group for example, —COO ⁇
• - for example, —COO—Ca—OCO
• alkaline earth metal ions As polyvalent metal ions, alkaline earth metal ions, transition metal ions, and the like can be used.
• Alkaline earth metal ions include beryllium, magnesium, calcium, strontium and barium ions.
• Preferred aqueous solutions containing alkaline earth metal ions include aqueous solutions of calcium chloride, calcium nitrate, calcium hydroxide, calcium oxide, magnesium chloride, magnesium nitrate, etc. Among them, an aqueous solution of calcium chloride is preferable.
• the transition metal ion is not limited as long as it is incorporated into the water-absorbing polymer, and examples thereof include ions of iron, cobalt, nickel, copper, and the like.
• Examples of the aqueous solution containing a transition metal ion include aqueous solutions of transition metal inorganic acid salts, organic acid salts, complexes, and the like. From the viewpoint of cost and availability, an aqueous solution of an inorganic acid salt or an organic acid salt is preferable.
• inorganic acid salts include iron salts such as iron chloride, iron sulfate, iron phosphate and iron nitrate, cobalt salts such as cobalt chloride, cobalt sulfate, cobalt phosphate and cobalt nitrate, nickel salts such as nickel chloride and nickel sulfate, Examples thereof include copper salts such as copper chloride and copper sulfate.
• organic acid salts include iron lactate, cobalt acetate, cobalt stearate, nickel acetate, and copper acetate.
• an aqueous solution of a calcium compound is preferable in consideration of safety and price.
• ozone used in the subsequent process has the property of decomposing on the alkali side, so an aqueous solution of calcium chloride that is weakly alkaline as close to neutral as possible is stronger than calcium hydroxide or calcium oxide, which is a strong alkali. preferable.
• the pH of the aqueous solution containing polyvalent metal ions is not particularly limited, but is preferably 11 or less. In the case of using an alkaline compound, the pH of the aqueous solution is preferably greater than 7 and 11 or less.
• the amount of the polyvalent metal ion is preferably 4 mmol or more, more preferably 4.5 to 10 mmol, further preferably 5 to 8 mmol, per 1 g (dry mass) of the superabsorbent polymer. If the amount of polyvalent metal ions is too small, dehydration of the superabsorbent polymer will be insufficient. If the amount of polyvalent metal ions is too large, excess polyvalent metal ions remain in the treatment liquid without being taken into the superabsorbent polymer, leading to wasted polyvalent metal salts and increasing the treatment cost.
• the concentration of the polyvalent metal ion in the aqueous solution containing the polyvalent metal ion is not particularly limited as long as it is a concentration at which the polyvalent metal ion is taken into the superabsorbent polymer, but is preferably 10 to 1000 mmol / L, more preferably. 50 to 700 mmol / liter, more preferably 200 to 400 mmol / liter. If the concentration is too low, dehydration of the superabsorbent polymer will be insufficient. If the concentration is too high, excess polyvalent metal ions remain in the treatment liquid without being taken into the superabsorbent polymer, leading to wasted polyvalent metal ions and increasing the treatment cost.
• the concentration of calcium chloride is preferably 1% by mass or more, but even if it is increased to 10% by mass or more, the effect does not change. Is preferably 10 to 10% by mass, more preferably 3 to 6% by mass.
• the pH of the acidic aqueous solution is 2.5 or less, preferably 0.5 to 2.5, and more preferably 1.0 to 2.4. If the pH is too high, the superabsorbent polymer may be insufficiently dehydrated. If the pH is too low, the pulp fibers recovered due to strong acid may be damaged.
• any aqueous solution of an inorganic acid or an organic acid can be used as long as the pH is 2.5 or less.
• the organic acid include tartaric acid, glycolic acid, malic acid, citric acid, succinic acid, and acetic acid, and citric acid is preferable.
• the concentration of the organic acid in the aqueous solution is not particularly limited as long as the pH is 2.5 or less, but is preferably 0.1 to 10.0% by mass, more preferably 0.8. It is 5 to 8.0% by mass, and more preferably 1.0 to 5.0% by mass. If the concentration is too low, the superabsorbent polymer may be insufficiently dehydrated. If the concentration is too high, organic acid may be wasted.
• the amount of the aqueous solution used in the decomposition step is not particularly limited as long as a physical force can be applied to the used sanitary products, but preferably 3 to 50 kg with respect to 1 kg of used sanitary products including filth. More preferably, it is 3 to 10 kg. If the amount of the aqueous solution is too small, the used sanitary goods cannot be effectively stirred in the aqueous solution. An excessive amount of aqueous solution leads to waste of polyvalent metal ions or acids and increases processing costs.
• the temperature of the aqueous solution used in the decomposition step is not particularly limited as long as the superabsorbent polymer is dehydrated, but is usually higher than 0 ° C. and lower than 100 ° C. Room temperature is sufficient, but heating may be used to increase the reaction rate. In the case of heating, room temperature to 60 ° C. is preferable, room temperature to 40 ° C. is more preferable, and room temperature to 30 ° C. is further preferable.
• the time for the decomposition step is not particularly limited as long as it is sufficient for the used sanitary goods to be decomposed, but is preferably 5 to 60 minutes, more preferably 10 to 50 minutes, and still more preferably 20 ⁇ 40 minutes.
• the method of the present invention includes a step of separating pulp fibers from a mixture of pulp fibers and other materials produced in the decomposition step (hereinafter also simply referred to as “separation step”).
• the pulp fibers are separated from a mixture of pulp fibers generated by the decomposition of the used sanitary goods and other materials (superabsorbent polymer, nonwoven fabric, plastic film, rubber, etc.).
• this step at least a part of the pulp fiber is separated and recovered. Not all of the pulp fibers need be recovered.
• other materials may be separated and recovered together with the pulp fibers.
• usually, at least a part of the superabsorbent polymer is mixed into the separated pulp fiber.
• the decomposed constituent material is separated into a fraction containing pulp fibers and a superabsorbent polymer and a fraction containing a nonwoven fabric, a plastic film and rubber.
• the fraction containing pulp fiber and superabsorbent polymer may contain some nonwoven fabric, plastic film and rubber, and the fraction containing nonwoven fabric, plastic film and rubber will contain some pulp fiber and superabsorbent polymer. May be included.
• the method for separating pulp fibers is not limited, but, for example, a method for separating and separating in water using a difference in specific gravity of decomposed constituent materials, and having a predetermined mesh of constituent materials having different sizes. Examples thereof include a method of separating through a screen and a method of separating with a cyclone centrifuge.
• the method of the present invention includes a step of treating the separated pulp fiber with an ozone-containing aqueous solution having a pH of 2.5 or less (hereinafter also referred to as “ozone treatment step”).
• the separated pulp fibers are mixed with a high water-absorbing polymer.
• the superabsorbent polymer remaining in the separated pulp fibers is removed by decomposing, reducing the molecular weight, and solubilizing.
• the ozone-containing aqueous solution having a pH of 2.5 or less used in this step is not particularly limited as long as it is an aqueous solution in which ozone is dissolved and has a pH of 2.5 or less.
• the pH may be adjusted to 2.5 or less by addition, or ozone may be dissolved by blowing ozone into an acid aqueous solution having a pH of 2.5 or less.
• ozone water refers to water in which ozone is dissolved.
• the ozone water can be prepared by using, for example, an ozone water generator (such as an ozone water exposure tester ED-OWX-2 manufactured by Ecodesign Corporation, an ozone generator OS-25V manufactured by Mitsubishi Electric Corporation).
• the ozone concentration in the ozone-containing aqueous solution is not particularly limited as long as it is a concentration capable of decomposing the superabsorbent polymer, but is preferably 1 to 50 ppm by mass, more preferably 2 to 40 ppm by mass, More preferably, it is 3 to 30 ppm by mass. If the concentration is too low, the superabsorbent polymer cannot be completely solubilized and the superabsorbent polymer may remain in the recovered pulp fiber. On the other hand, if the concentration is too high, the oxidizing power is also increased, which may damage the pulp fiber and may cause a problem in safety.
• the treatment time of the ozone treatment process is not particularly limited as long as it is a time during which the superabsorbent polymer can be decomposed.
• the treatment time may be short if the ozone concentration in the ozone-containing aqueous solution is high, and a long time is required if the ozone concentration in the ozone-containing aqueous solution is low.
• the product of the ozone concentration (ppm) in the ozone-containing aqueous solution and the treatment time (minute) of the ozone treatment step (hereinafter also referred to as “CT value”) is preferably 100 to 6000 ppm ⁇ min, more preferably 200 to 4800 ppm. Min., More preferably 300 to 3600 ppm ⁇ min.
• the treatment time of the ozone treatment step depends on the ozone concentration in the ozone-containing aqueous solution, preferably 5 to 120 minutes, more preferably 10 to 100 minutes, and still more preferably. 20 to 80 minutes.
• the amount of the ozone-containing aqueous solution is not particularly limited as long as it is sufficient to completely immerse the separated pulp fibers, but is preferably 300 to 5,000 with respect to 100 parts by mass (dry basis) of the separated pulp fibers. Parts by mass, more preferably 500 to 4000 parts by mass, and still more preferably 800 to 3000 parts by mass. If the amount of the ozone-containing aqueous solution is too small, the superabsorbent polymer cannot be completely solubilized and the superabsorbent polymer may remain in the recovered pulp fiber. On the other hand, if the amount of the ozone-containing aqueous solution is too large, the production cost may increase.
• the method for treating the separated pulp fibers with the ozone-containing aqueous solution in the ozone treatment step is not particularly limited.
• the ozone-containing aqueous solution is put in a treatment tank, and the separated pulp fibers are put into the ozone-containing aqueous solution. That's fine.
• stirring of the ozone-containing aqueous solution is not essential, but it is preferable to stir appropriately.
• ozone gas may be blown into the aqueous solution placed in the container, and a flow may be generated in the ozone water by raising the bubbles of the ozone gas.
• the temperature of the ozone-containing aqueous solution is not particularly limited as long as it is a temperature capable of decomposing the superabsorbent polymer, and the ozone-containing aqueous solution may be heated, but may be kept at room temperature.
• the superabsorbent polymer In the ozone treatment process, the superabsorbent polymer is subjected to the oxidative decomposition action by ozone, the three-dimensional network structure of the superabsorbent polymer is destroyed, and the superabsorbent polymer loses its water retention, has a low molecular weight and is solubilized.
• the superabsorbent polymer having increased fluidity dissolves in the ozone-containing aqueous solution. Furthermore, in this process, pulp fibers are disinfected, bleached, and deodorized by the disinfection action of ozone.
• the ozone-containing aqueous solution has a pH of 2.5 or less. That is, the ozone treatment process is performed in an acidic state with a pH of 2.5 or less.
• an acidic ozone-containing aqueous solution By using an acidic ozone-containing aqueous solution, the water absorption expansion of the superabsorbent polymer can be suppressed, and the decomposition and removal effect of the superabsorbent polymer by ozone is dramatically improved. Can be disassembled.
• the decomposition step when an aqueous solution containing polyvalent metal ions is used, the superabsorbent polymer is dehydrated by polyvalent metal ions, so that the superabsorbent polymer can absorb water without using an acidic ozone-containing aqueous solution.
• an aqueous solution having a pH of 2.5 or less is used to dissolve and remove the polyvalent metal adhering to the surface of the pulp fiber with an acid.
• an acidic aqueous solution having a pH of 2.5 or less is used in the decomposition step
• the reason why the aqueous solution having a pH of 2.5 or less is used in the ozone treatment step is to suppress the water absorption expansion of the superabsorbent polymer. is there.
• the disinfection effect by an acid can also be provided by processing with acidic ozone containing aqueous solution.
• the pH of the ozone-containing aqueous solution is preferably 0.5 to 2.5, and more preferably 1.0 to 2.4.
• An ozone-containing aqueous solution having a pH of 2.5 or less can be produced by adding an acid to ozone water.
• the acid is not particularly limited, and an inorganic acid and an organic acid can be used, but an organic acid is preferable. Since organic acids function in a weak acid range and are environmentally friendly, organic acids are preferred from the viewpoint of safety and environmental burden. Although it does not specifically limit as an organic acid, Tartaric acid, glycolic acid, malic acid, a citric acid, a succinic acid, an acetic acid etc. can be mentioned. Of these, citric acid is preferred.
• the pH of the ozone-containing aqueous solution can be adjusted depending on the type of acid and the amount of acid added.
• the concentration of the organic acid in the ozone-containing aqueous solution is not limited as long as the pH is within a predetermined range, but is preferably 0.1 to 5.0% by mass, more preferably 0.2 to 3.0% by mass. %, And more preferably 0.5 to 2.0% by mass.
• the ozone treatment step is performed in an acidic state with a pH of 2.5 or less.
• the alkaline calcium compound may remain in the pulp fiber subjected to the ozone treatment step, and when the pulp fiber is added to the ozone-containing aqueous solution, The pH of the aqueous solution may change.
• the pH of the ozone-containing aqueous solution here refers to the pH of the ozone-containing aqueous solution after adding the pulp fiber.
• the pH can be adjusted by, for example, adding pulp fibers and an ozone-containing aqueous solution to the treatment tank, adding acid thereto while stirring, and adding the acid when the pH of the solution in the treatment tank reaches a predetermined pH. Stop.
• citric acid is particularly preferable.
• an aqueous solution containing calcium ions is used in the decomposition step, calcium ions and various calcium compounds are attached to the surface of the separated pulp fibers.
• Calcium compounds adhering to pulp fibers are not necessarily water-soluble, but also include insoluble and poorly soluble compounds, and cannot be removed by washing alone. Since citric acid forms a chelate with calcium and becomes water-soluble calcium citrate, insoluble or hardly soluble calcium compounds adhering to the surface of the pulp fiber can be effectively dissolved and removed.
• citric acid can form chelates with metals other than calcium, when insoluble or hardly soluble metal compounds other than calcium compounds are attached to the surface of the pulp fiber, not only calcium compounds but also calcium compounds Other insoluble or hardly soluble metal compounds can be dissolved and removed. As a result, the ash content of the obtained recycled pulp can be reduced.
• citric acid shows acidity, the pH of the recycled pulp can be controlled in a weakly acidic range depending on the condition setting including the washing step, and is gentle to the skin.
• citric acid is not a harmful substance for the human body, safety is high even if citric acid remains in the obtained recycled pulp.
• citric acid is a mild weak acid compared to the acid used in pulp refining, damage to the resulting recycled pulp can be reduced.
• citric acid can be obtained relatively inexpensively, recovery and regeneration costs can be reduced.
• citric acid does not smell and does not deteriorate the working environment. Sixth, there is no need for large-scale capital investment, and the current equipment can be used.
• the method of the present invention may include steps other than the decomposition step, the separation step, and the ozone treatment step, between the decomposition step and the separation step, between the separation step and the ozone treatment step, or before and after each step.
• processes other than the decomposition process, separation process, and ozone treatment process include processes such as cleaning, dehydration, disinfection, and measurement.
• the method of the present invention preferably includes a step of dehydrating the separated pulp fibers (hereinafter also referred to as “pulp fiber dehydration step”) between the separation step and the ozone treatment step.
• the method for dewatering the separated pulp fibers is not limited, and can be performed, for example, by dehydrating the separated pulp fibers with a dehydrator such as a centrifuge.
• the dehydration conditions are not particularly limited as long as the moisture content can be lowered to the target value.
• the dehydration time is preferably 1 to 10 minutes, more preferably 2 to 8 minutes, Preferably it is 3 to 6 minutes.
• the method of the present invention may include a step of washing recycled pulp with water (hereinafter also referred to as “recycled pulp washing step”) following the ozone treatment step.
• the method of the present invention may include a step of dehydrating the recycled pulp (hereinafter also referred to as “recycled pulp dehydration step”) following the recycled pulp washing step.
• the recycled pulp washing step and the recycled pulp dewatering step may be performed once, or may be alternately repeated a plurality of times.
• the method of the present invention may optionally include a step of drying the recycled pulp pulp (hereinafter also referred to as “recycled pulp drying step”) following the recycled pulp dewatering step.
• the dried recycled pulp is preferably processed and reused in a form suitable for a sanitary article manufacturing facility, such as a sheet, a roll, or a lump.
• the specific example of the process flow which manufactures recycled pulp from used sanitary goods using the method of this invention is as follows. (1) Weigh the used paper diaper (weighing step). (2) A used paper diaper and a 5% concentration calcium chloride aqueous solution are put into a washing machine, and the paper diaper is disassembled by stirring impact while being washed in the manner of a vertical washing machine (decomposing step). (3) Separating into a fraction containing pulp fibers and superabsorbent polymer and a fraction containing non-woven fabric, plastic film and rubber (separation step). (4) The recovered pulp fiber and superabsorbent polymer are dehydrated (dehydration step).
• the pulp fiber and superabsorbent polymer after dehydration are immersed in an organic acid (for example, citric acid) aqueous solution having a pH of 2.5 or less (calcium removal and acidification), and the ozone treatment is performed with an acid that is difficult to deactivate ozone. (Dissolve superabsorbent polymer, disinfect, bleach and deodorize) (ozone treatment step).
• organic acid for example, citric acid
• ozone treatment step Dissolve superabsorbent polymer, disinfect, bleach and deodorize
• Another specific example of the process flow for producing recycled pulp from used sanitary goods using the method of the present invention is as follows. (1) Weigh the used paper diaper (weighing step). (2) A used paper diaper and an aqueous citric acid solution having a concentration of 10% are put into a washing machine, and the paper diaper is decomposed by a stirring shock while being washed in the manner of a vertical washing machine (decomposing step). (3) Separating into a fraction containing pulp fibers and superabsorbent polymer and a fraction containing non-woven fabric, plastic film and rubber (separation step). (4) The recovered pulp fiber and superabsorbent polymer are dehydrated (dehydration step).
• pulp fibers including residual superabsorbent polymer
• other materials including plastic film, non-woven fabric, etc.
• pulp fibers including residual superabsorbent polymer.
• ozone treatment By performing ozone treatment on the surface, dirt can be washed, the organic matter concentration is low, and there is no ozone gas shielding material such as plastic film, so that it can be treated easily and in contact with ozone. Can be performed, processing time is reduced, and recycled pulp with lower ash content than unused pulp can be produced.
• the ozone treatment target can be limited to some extent, it is easy to set a reliable sterilization level, and it is possible to prevent the production of harmful substances (mutagenic substances, etc.) due to the oxidative decomposition of ozone.
• the present invention it is possible to efficiently collect ash pulp that conforms to the hygiene material standards. Since the superabsorbent polymer has a low molecular weight and is solubilized by the ozone treatment, the superabsorbent polymer does not remain between the pulp fibers.
• citric acid is used in the ozone treatment process, calcium can be dissolved and removed by the chelating effect of citric acid, and the ash derived from the superabsorbent polymer (calcium cross-linked product) inactivated by calcium is recovered. Not detected in recycled pulp.
• the recycled pulp obtained by the method of the present invention is preferably recycled pulp having an ash content of 0.65% by mass or less and reusable for sanitary napkins. Further, according to the present invention, the foreign matter contained in the unused pulp can be removed by treating with an ozone-containing aqueous solution having a pH of 2.5 or less, so that the ash content is lower than the ash content of the unused pulp. Recycled pulp can also be obtained.
• the recycled pulp obtained by the method of the present invention preferably has an ash content of 0.11% by mass or less, and more preferably has an ash content of 0.05 to 0.11 mass. The method for measuring ash will be described later.
• the recycled pulp obtained by the method of the present invention is preferably used for at least one of an absorbent body, a tissue and a nonwoven fabric constituting a sanitary product.
• Example 1 A commercially available disposable diaper (Moonie M size manufactured by Unicharm Corporation) was soaked and absorbed in 3 L of physiological saline containing 1% artificial filth for 10 minutes, and then added to a 5% strength aqueous calcium chloride solution (pH 10.5). It was immersed for a minute and the SAP in the diaper was dehydrated by Ca cross-linking action.
• a commercially available disposable diaper (Moonie M size manufactured by Unicharm Corporation) was soaked and absorbed in 3 L of physiological saline containing 1% artificial filth for 10 minutes, and then added to a 5% strength aqueous calcium chloride solution (pH 10.5). It was immersed for a minute and the SAP in the diaper was dehydrated by Ca cross-linking action.
• the ash content of the pulp (hereinafter also referred to as “unused pulp”) originally contained in the commercially available paper diapers used in the examples and comparative examples was 0.18% by mass.
• Example 2 A commercially available disposable diaper (Moonie M size manufactured by Unicharm Corporation) was soaked and absorbed in 3 L of physiological saline containing 1% of artificial filth for 10 minutes, and then added to a 10% aqueous citric acid solution (pH 1.6). It was immersed for a minute, and the SAP in the diaper was dehydrated by the action of acid.
• a commercially available disposable diaper (Moonie M size manufactured by Unicharm Corporation) was soaked and absorbed in 3 L of physiological saline containing 1% of artificial filth for 10 minutes, and then added to a 10% aqueous citric acid solution (pH 1.6). It was immersed for a minute, and the SAP in the diaper was dehydrated by the action of acid.
• Comparative Example 1 After 200 mL of sanitary saline was absorbed in a commercially available disposable diaper (Muninie's “Mooney” M size), the disposable diaper was placed in the washing layer of a two-tank type small washing machine (Aluminus “Sunny” AST-01). 8 pieces are added, and 80 g of calcium oxide (CaO) (manufactured by Wako Pure Chemical Industries, Ltd.) is subsequently added, and then a sodium hypochlorite aqueous solution (concentration 250 ppm, manufactured by Wako Pure Chemical Industries, Ltd.). (Diluted sodium with tap water) 6.5 L was added.
• CaO calcium oxide
• a sodium hypochlorite aqueous solution concentration 250 ppm, manufactured by Wako Pure Chemical Industries, Ltd.
• Comparative Example 2 A commercially available paper diaper (Moonie M size manufactured by Unicharm Corporation) was immersed in 3 L of physiological saline containing 1% artificial filth for 10 minutes, and then 10 L of a 1% aqueous citric acid solution (pH 2.2) was added. Then, 80 mg / m 3 of ozone gas was blown in for 30 minutes. The dissolved ozone amount of the treated water after 30 minutes was 1 ppm and pH 3.0. In this comparative example, since ozone was consumed for the decomposition of the artificial filth, the amount of dissolved ozone in the treated water after 30 minutes was lower than that in Example 1 or Example 2.
• Table 1 summarizes the results of measuring the ash content, water absorption performance and water retention performance of the pulps recovered in the examples and comparative examples.
• the measuring methods of ash content, water absorption performance, and water retention performance are as follows.
• the ash content, absorption performance and water retention performance of the pulp originally contained in the commercially available paper diapers used in the examples and comparative examples were 0.18% by mass, 16.4 g / g and 7.60 g / g. .
• Ash refers to the amount of inorganic or incombustible residue left after organic matter has been ashed. Ash content is measured in accordance with “5. Ash test method” in “2. That is, the ash content is measured as follows. A platinum, quartz, or magnetic crucible is ignited in advance at 500 to 550 ° C. for 1 hour, allowed to cool, and then its mass is accurately measured. Take 2 to 4 g of sample, place in crucible, weigh accurately, remove or shift crucible if necessary, heat gently at first, gradually increase temperature to 500-550 ° C. Ignite for over an hour until no carbides remain. After standing to cool, weigh its mass precisely. The residue is incinerated until it reaches a constant weight, and after standing to cool, its mass is precisely measured to obtain the amount of ash (%).
• Water absorption performance refers to the mass of water absorbed by pulp fibers per unit mass, and is measured as follows. (1) A bag (200 mm ⁇ 200 mm) of a nylon net (250 mesh nylon net manufactured by NBC Meshtec Co., Ltd.) is prepared, and its mass N 0 (g) is measured. (2) About 5 g of a measurement sample is put into a nylon net, and the mass A 0 (g) including the bag of the nylon net is measured. (3) Put 1 L of 0.9% physiological saline in a beaker and immerse the prepared nylon net bag containing the sample for 3 minutes. (4) Pull up the bag, leave it on the draining net for 3 minutes, and drain it.
• a nylon net 250 mesh nylon net manufactured by NBC Meshtec Co., Ltd.
• the mass A (g) after draining the nylon net bag containing the sample is measured.
• (6) Prepare another set of nylon nets cut out at the same size, carry out (3) and (4) in the same way without putting a sample, and mass N (g of nylon net bag after draining ).
• the mass ratio is preferably 100% or less, more preferably 90% or less, and still more preferably 80% or less.
• the recycled pulp produced by the method of the present invention can be suitably used again for the production of sanitary products.

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